hw/arm/virt: add secure memory region and UART

Add a secure memory region to the virt board, which is the
same as the nonsecure memory region except that it also has
a secure-only UART in it. This is only created if the
board is started with the '-machine secure=on' property.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Acked-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>

include/hw/arm/virt.h

@@ -60,6 +60,7 @@ enum {
     VIRT_PLATFORM_BUS,
     VIRT_PCIE_MMIO_HIGH,
     VIRT_GPIO,
+    VIRT_SECURE_UART,
 };
 
 typedef struct MemMapEntry {